Rebels taking a province at war

This site doesn't give overall pointers, but I can explain why you might be losing with superior numbers. There are a couple reasons that this could be happening. They could have better military tech than you. I doubt this is the case since it sounds like you are talking about early game and you shouldn't fall far behind aragon in general. They could have better leaders than you, make sure you assigned a leader. They could be simply very lucky, although this is unlikely with armies as big as the ones you mentioned. They may have a better army composition than you (50 percent inf/cav and 50 percent artillery is stronger than 100 percent inf/cav).

If you are the attacker, you also could be penalized for crossing a river, attacking into mountains or desert, or winter.

If you post a couple screenshots of the battle overview (the box that shows the troop formations and penalties and leader bonuses) I can probably explain the exact problem for you.

If one of your provinces belongs to HRE but your nation is not a part of HRE and you make that province leave the HRE then the following effects would occur

• Relationship with Emperor -50

The province must be a core province to enable the ability to make a province leave the HRE.

Not sure if it stacks.

Having a province within the HRE increases your Imperial Authority. This in turn allows you to pass reforms if you ever become the Emperor of the HRE further down the line.

Any provinces bordering the HRE (including 1 sea province) may ask to join the HRE unless your nation is more powerful than the current Emperor.

If your capital is a member of HRE you become a prince of HRE and therefore can be elected Emperor. This has it's own benefits.

If you're annexing HRE provinces then it is best to core them as soon as possible as the Emperor will soon declare them "unlawful territory" and demand there return when not cored. If you refuse you get -33 relations with Emperor, -10% production and -50% manpower within the province concerned.